This invention is directed to a process for producing mineral wool from molten slag which has been formed in a cyclone-like furnace. In the process, a first particulate material containing combustibles having heat values and non-combustibles are fed with a second particulate material containing fluxstone and preheated air into a a cyclone-like furnace wherein the combustibles are substantially instantaneously burned and the non-combustibles and fluxstone are melted and reacted to form a molten slag suitable for fiberizing into mineral wool. More particularly, the invention is directed to a process in which particulate waste coal products containing organic combustibles having heat values and inorganic non-combustibles and lime waste products containing fluxstone are fed with preheated air into a high temperature furnace wherein the combustibles are substantially instantaneously burned and the non-combustibles and fluxstone are melted and reacted to form a molten slag of a desired composition, which slag is fiberized into mineral wool.
Mineral wool is an inorganic amorphous fibrous solid silicate material containing varying percentages of metallic oxides, particularly of silicon, aluminum, iron, magnesium and calcium with incidental percentages of manganese, titanium, sulfur and the like. Mineral wool is a generic term which includes rock wool which is made from rocks and/or slags, slag wool which is made from slags produced in certain processes, for example iron and steel making, and glass wool. Rock wool and slag wool usually have a silica plus alumina content which is between about 45 to 55 weight percent and typically contain 32 to 45 weight percent silica whereas glass wool has a silica plus alumina content of at least about 70 weight percent, and may be as much as 80 weight percent, and a silica content of 55 to 75 weight percent. Mineral wools may be used for insulation against heat and cold and for sound absorption.
Rock wools are made from molten slags produced in a suitable furnace wherein naturally occurring rocks and/or slags having the requisite chemical composition are melted by means of burning coke or by electrical energy. In the cupola or vertical shaft furnace process, naturally occurring materials, for example argillaceous limestone, calcareous shale and mixtures of such materials, together with coke constitute the charge delivered into the cupola or vertical shaft furnace. The coke burns and melts the rocks or minerals in the burden producing a liquid slag having the required composition. Cupolas, which are used to produce the liquid slags, have a low unit capital cost, are thermally efficient and can be started and stopped relatively quickly. However, the operation of the cupola can be erratic. Although the composition of the slag can be regulated by varying the composition of the burden, the effects of any such variations are not noticeable for one hour or more. As a result it is possible that large quantities of off-composition liquid slag can be produced. It is also possible to increase or decrease the temperature in the cupola by increasing or decreasing the proportion of coke in the burden or by varying the temperature of the air introduced into the bottom of the furnace if preheated air is used to aid combustion. However, the effects of such changes are not realized immediately but occur over a considerable time span, for example at least one hour.
Mineral wools have also been prepared from waste products, such as fly ash produced during combustion of pulverized coal in the boilers of power generating plants and from waste materials produced during the processing of natural rocks and minerals. One such process, described in U.S. Pat. No. 2,020,403 issued in 1935 to Isaiah B. Engle entitled "Process for Producing Mineral Fiber", is directed to a process for producing mineral fiber in which waste limestone fines and waste clay particles are mixed and extruded into briquettes which are charged into a cupola-like furnace and from which by the use of a suitable fuel a molten slag is produced which may be processed into mineral fiber. Various fuels may be used as a part of the briquettes or may be charged as a separate material between the briquettes. The preferred fuel is a very fine waste coal known as anthracite culm or fine waste coke known as coke breeze. Other fuels, such as oil, coal or gas, may also be used in the process. The mixture is ignited and air is blown upwardly through the burden. The briquettes are readily and quickly heated to a high temperature causing the articles to melt and form a molten slag. The slag flows downwardly in the furnace and is discharged through a port formed near the bottom of a wall of the furnace. The thus discharged molten slag is propelled through the air at relatively high speed to form thread-like fibers which are collected in the form of wool. The fibers are processed into batts or other forms which are commercially usable. During fiberization, a portion of the slag forms in the shape of small spherical particles which are referred to as shot. The shot is collected and recycled in the process. The mineral fiber thus produced has a composition of 35 to 45 weight percent silica; 10 to 20 weight percent alumina; 5 to 8 weight percent ferric oxide; 15 to 25 weight percent lime and 8 to 25 weight percent magnesia.
The process described above is subject to the problems of producing molten slags in cupola furnaces as mentioned above. Additionally, the waste limestone fines utilized in the process have compositions which can vary widely dependent upon the location from which they were quarried. As a result, the compositions of the molten slags produced from these waste products are not uniform. To produce molten slags of essentially similar compositions, it is necessary to carefully select the waste material used in the process.
Molten slags of more uniform composition than are prepared as described above can be prepared by melting rocks or minerals in electric furnaces. Electric furnaces are amenable to close control of the melting process. Maintenance or adjustment of the temperature and composition of the liquid slag is more easily made and the results are more quickly realized than in cupola melting. Electric energy is, however, expensive and the original capital cost of an electric furnace and attendant equipment is relatively high. Therefore, electric furnaces are used where electric energy is relatively cheap when compared to the use of coke as a fuel.
The production of mineral wool directly from molten slags formed in ironmaking furnaces, steelmaking furnaces, non-ferrous melting furnaces and the like has been tried, but has not been commercially successful. Such slags generally are not of the required composition and additions of other materials are needed to obtain the required composition. The iron oxide content of the slags may be too high or too low for the type of mineral wool desired or the slag may have a high calcium oxide content whereby large additions of silica may be required to attain the desired chemistry.
There is, therefore, a need for a relatively inexpensive continuous process which is susceptible to close operational control wherein particulate combustibles are substantially instantaneously burned and particulate non-combustibles of a desired composition and particulate fluxstone are melted and reacted to form molten slags of a desired composition, which slags can be fiberized into mineral wool.
It is an object of this invention to provide a relatively low cost continuous process for producing molten slags of a desired composition which can be fiberized into mineral wool, which process is amenable to close operational control and has substantially instantaneous response to compositional and temperature controls.
It is another object of this invention to provide a process for producing molten slags of a desired composition and which are suitable for fiberizing into mineral wool wherein mixtures of a particulate material, such as waste coal tailings containing organic combustibles and inorganic non-combustibles and a particulate material, such as waste lime containing fluxstone and preheated combustion air are continuously charged into a high temperature furnace wherein the combustibles are substantially instantaneously burned at relatively high temperatures and the non-combustibles and fluxstone are melted and reacted to form molten slags which have the requisite composition, temperature and viscosity suitable to be fiberized into mineral wool.